Friday, November 23, 2007

Or at least, that's the implication of this BBC story about the latest neuroimaging paper (Fliessbach et al., 2007) in Science:

Men motivated by 'superior wage'[NOTE: so I guess women aren't, eh?we don't know, since they weren't tested]Brain scans show we measure our success by others' earnings

On receiving a paypacket, how good a man feels depends on how much his colleague earns in comparison, scientists say.

Scans reveal that being paid more than a co-worker stimulates the "reward centre" in the male brain.

What was the study actually about?

The absolute consumption level, or alternatively the absolute level of income, is the most important determinant of individual well-being in traditional economic models of decision-making. These models typically assume that social comparisons, and therefore relative income, play no role. This view has long been challenged by social psychologists and anthropologists, who have argued that comparison with other individuals is a central phenomenon within human societies...

OK, so we already know that social comparisons and relative income matter. What can we learn from this study? Is it much of a surprise that the participants were competitive?

Despite the importance of distinguishing the roles of absolute and relative income levels for subjective well-being, and thus for human decision-making, the underlying neurobiological basis of social comparison is not well understood.

Yeah, OK, stick people in a scanner and see what happens. What did the professional subjects do while there? Pairs of participants were scanned simultaneously in two different magnets while estimating the number of dots presented on a computer screen. After each trial, both participants received feedback on how each of them had done, and how much money was earned according to a predefined payment schedule. So what happened?

...conditions in which a subject solved the task correctly and received a payment while the other subject did not were contrasted with conditions in which a subject received no payment. This contrast yielded significant activation in three bilateral and three medial regions, which defined our regions of interest: left and right occipital cortex, left and right angular gyrus, left and right ventral striatum [see above figure], precuneus, and medial orbitofrontal cortex (two distinct activations), thus including the regions known to be critically involved in the processing of reward.

So all these other brain regions were activated as well. Why occipital cortex and angular gyrus? We'll never know, because the authors never discuss the significance of those responses. What was so distinctive about the ventral striatum, then?

According to our hypothesis, the parameter estimates increased with the ratio between a subject's reward and the other subject's reward... All other main effects and interactions of the ANOVA analysis turn out to be insignificant. This holds for the main effect of high versus low payment condition as well as its interaction with relative payment. The latter result suggests that the importance of relative comparison is independent of the level of payment. ... All posterior regions (occipital lobe, angular gyrus, and precuneus/cingulate cortex) showed a different pattern, with response intensity significantly varying with both absolute and relative payment. In these regions, responses were highest ... in situations when high amounts of money were unequally paid regardless of which of the subjects received more. A similar pattern was found in the two orbitofrontal regions.

In brief, the ventral striatum was uniquely related to greater relative reward (not just absolute reward). So what have we learned? It's rewarding to win a competition and to earn more money than a rival.

Reference

K. Fliessbach, B. Weber, P. Trautner, T. Dohmen, U. Sunde, C. E. Elger, A. Falk (2007). Social Comparison Affects Reward-Related Brain Activity in the Human Ventral Striatum. Science 318:1305-1308.Whether social comparison affects individual well-being is of central importance for understanding behavior in any social environment. Traditional economic theories focus on the role of absolute rewards, whereas behavioral evidence suggests that social comparisons influence well-being and decisions. We investigated the impact of social comparisons on reward-related brain activity using functional magnetic resonance imaging (fMRI). While being scanned in two adjacent MRI scanners, pairs of subjects had to simultaneously perform a simple estimation task that entailed monetary rewards for correct answers. We show that a variation in the comparison subject's payment affects blood oxygenation level–dependent responses in the ventral striatum. Our results provide neurophysiological evidence for the importance of social comparison on reward processing in the human brain.

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Born in West Virginia in 1980, The Neurocritic embarked upon a roadtrip across America at the age of thirteen with his mother. She abandoned him when they reached San Francisco and The Neurocritic descended into a spiral of drug abuse and prostitution. At fifteen, The Neurocritic's psychiatrist encouraged him to start writing as a form of therapy.